If you want to claim the rest or some of the remaining tricks, you press Claim - bottom right.
Give the number of tricks you claim and a line of play.
In the chat bar shows your line of play.
If no line of play given it'll show in the chat bar:
Claimer Alias > No line of play.
Claim No Trump Contract
Claim Suit Contract
To Accept or Decline a Claim, press the appropriate button, bottom right
Defender Claim (Concession)
Our policy is that a defender can claim a number of tricks less than all remaining tricks, for which they will need the consent of their partner. This is to stop a defender claiming all tricks by accident, and declarer accidentally accepting.